docs: def get(self, key, mem_map=True):
          """
          Read and return the data stored for the given key.
  
          Args:
              key (str): The key to read the data from.
              mem_map (bool): If ``True`` returns the data as
                              memory-mapped array, otherwise a copy is returned.
  
          Note:
              The container has to be opened in advance.
  
          Returns:
              numpy.ndarray: The stored data.
          """
          self.raise_error_if_not_open()
  
          if key in self._file:
              data = self._file[key]
  
              if not mem_map:
                  data = data[()]
  
              return data
          else:
              return None